Integrated optical systems combine a light receiving structure with circuitry for evaluation of the received signal on a single chip. This allows minimum feature sizes and compact, multifunctional designs. With progressing miniaturization, there is a challenge to uphold high fill factors (i.e., the ration between active area and overall area of a photosensitive pixel), since wiring and peripheral circuitry limits the area that is left for photo detection. Furthermore, a portion of the light is reflected or absorbed in the region of peripheral circuitry. This share of the photosensitive pixel is unused and the overall sensitivity of the device is reduced.
Currently, a one way to provide a higher fill factor is the implementation of curved micro lenses. Incoming light is focused by a curved micro lens to the active area of a photo sensor pixel. However, this setup is elaborate in fabrication and the curved shape of the micro lens limits the combination with other elements. The use of the curved micro lens is especially limited when there is a need of spectral filters, as the deposition of the latter is difficult due to the rounded surfaces of the lenses.
Therefore, an improved device having a higher fill factor and an increased sensitivity without the use of a curved structure may be desirable.